Packet detection may be done via autocorrelation, which is correlation of a received signal with its delayed version; and cross-correlation, which is correlation of the received signal with an expected signal. The expected signal is the transmitted reference signal that is complex conjugated and order-reversed.
Autocorrelation is more robust to echoes, but its peak is not adequately sharp and it is susceptible to any periodic signal with the same period as the delay of the autocorrelation. On the other hand, cross-correlation is sensitive to channel echoes and frequency offset but its peak is distinctive.
Accordingly, a new apparatus and method are needed for packet detection.